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The Maximum Occupant Load in the Building Code – Not a Maximum

Sean O'Hara — Thu, 19 Jan 2012 21:00:43 +0000

There is a common misconception about the "Maximum" Occupant Load table in the International Building Code. This table list the number of occupants per square foot that you are designing to rather than a true maximum.

As an example, the table lists 100 gross sf per occupant in a business occupancy. If you have a 1,000 sf office then you are designing for 10 occupants. However, the 10 really functions as a minimum rather than a maximum. You must design adequate exiting and fixture count for 10 occupants.

If your space is actually designed for more occupants that's absolutely fine as long as you are following all of the code provisions for more occupants. In this example if your 1,000 sf is a call center with 25 people, then you need to make sure your exiting, plumbing, mechanical and so forth are designed to handle 25. You just have to make sure you don't exceed 1 person per 7 square feet, that's an absolute maximum and very tight quarters. I've never seen it, but the code official can ask you to show a diagram for your increased occupant load.

On the other end of the spectrum, you can actually design for less that the maximum occupant load, but only with approval of the building department, and I've never seen this happen.

The code section uses the phrase "design occupant load" and that is really a more accurate phrase.

Originally posted 2009-09-26 00:01:19.

Lose Weight Today! Ask Me How. – Steel Beams

Adam Denton — Thu, 19 Jan 2012 21:00:29 +0000

I apologize if the title is misleading. The weight I am talking about is the weight of steel beams. Why am I concerned about the weight of steel beams you may ask? The answer is that steel product suppliers typically price steel beams in terms of pounds of steel. The stronger a beam is, typically the more it weighs, thus the more it costs. My goal as your structural engineer is to ensure that you are not paying too much for your construction materials. I do this by making sure I am not specifying beams that are stronger than they need to be by using the load reductions allowed by the building code.

“Load reductions? Sounds dangerous… Don’t we need to account for ALL the loads?”

My answer is yes and no. As a structural engineer I do account for all the loads, but the code makes allowances for that fact that statistically, a structural framing member will not experience all the full loading conditions at one time.

For the sake of simplicity, let’s use a typical residential home as an example. It is common practice that all interior loads focus down through the house on to one longitudinal steel beam. This steel beam may support the main floor, the upper floor and possibly the roof. For this steel beam to experience the full loading conditions at the same time you would have to be having a house party where all the guests are rubbing shoulders and covering every square foot of both floors. That would mean people standing on your kitchen table and in your bath tub and sitting on your countertops. There is a very slim chance of this happening right? But, you still have to consider that this wild blowout is also taking place during the worst snow storm you have seen in ages for your roof to also simultaneously experience its full live loading condition. It isn’t much of a stretch of the imagination to think that this situation is never likely to occur.

The building code accounts for this by specifying a set of basic design load combinations. Below is an excerpt from the 2009 International Building Code. As these equations illustrate, when you consider a variety of loads at once you can reduce a percentage of certain loads. For each framing member designed we will consider each combination equation and chose the worst case to specify in our construction documents. That way our clients’ structures can “lose weight” and we can save them money.

Live loads may be further reduced beyond the load combinations mentioned above by using the provisions of section 1607.9 of the 2009 UBC.

Originally posted 2010-07-16 15:15:23.

Avoid Costly Future Alterations: Free Fair Housing and Accessibility Presentation

evstudio — Thu, 19 Jan 2012 21:00:18 +0000

This week the Department of Local Affairs (DORA) Civil Rights Division offered one of four free lectures on Fair Housing, Accessibility and Reasonable Accommodations. The lecture is given by DORA's fair housing expert, Jennifer McPherson, she covers the local, state and federal fair housing regulations.

This is a must see for architects, real estate agents, housing property managers, and owners of rental housing. In addition to the free lecture DORA provides stacks of detailed brochures and other materials you can take and hand out at your office to build awareness.

The material covered in this presentation includes an overview of the many levels of fair housing regulations, how they overlap and how to be sure you comply. Fair Housing regulations cover a broad range of classes and vary at the Federal, State and Local level.

Federal Law requires that one can not discriminate based on:

Race
Color
Religion
Sex
Handicap (disabilities)
Familial Status
National Origin

Colorado State Law adds:

Marital Status
Creed
Ancestry
Sexual Orientation

Local Ordinances (City and County of Denver) add yet again:

Age
Military Status
Gender Variance

Keeping in mind that fair housing covers many different protected classes the most common issue for architects is disability. Many of the discussions I have had with clients that must provide accessibility in their buildings revolve around the loss of square footage in a living room or bedroom due to more space required in bathrooms and kitchens. Of course, if these requirements are carried out within the building it could result in very costly alterations in the future in order to comply. During this lecture you are given clear ideas of how to communicate why these requirements are necessary.

Educating architects, real estate agents, developers and owners on this topic is one way to ensure we are preventing future noncompliance. This key for the DORA Civil Rights Division because currently the division is a reactionary or complaint-driven agency. Meaning, the division needs to improve its education and outreach to transform into a more preventative department.

The more we can educate our clients the more we can provide fair housing! The next FREE lecture is June 1st 9:30 am-11:30 am offered at 1560 Broadway, Conference Room 110 B (first floor), Denver. The following two lectures are offered September 7, 2010, 9:30 a.m. - 11:30 a.m. and November 2, 2010, 9:30 a.m. - 11:30 a.m. at the same location.

Another helpful organization to check out is Fair Housing Accessibility First. This site gives you a detailed look at design and construction requirements with regard to accessibility.

Originally posted 2010-04-13 00:01:57.

Seismic Testing of a Mid-Rise Wood Framed Structure

Adam Denton — Thu, 19 Jan 2012 20:59:46 +0000

NEESWood Capstone Test Structure

After the destruction caused by the 1995 Kobe earthquake the Japanese government took it upon themselves to construct the world’s largest seismic testing table, often referred to as a “shake table”. This testing facility, called Earth-Defense, was built to its enormous size out of necessity. Space to build new structures is a rare commodity in Japan and it was essential to be able to test large mid-rise (4 to 7 story) structures that maximize usable space while minimizing the building footprint. The Earth-Defense shake table is 50’ x 65’ and can support an astonishing 2.5 million pounds while “shaking” test buildings in three directions at once.

The NEESWood Capstone project shown in this video was conducted last summer to test the viability of wood framed mid-rise structures. Mid-rise structures are more traditionally constructed out of steel and concrete, but with the trend towards “green” construction it is becoming desirable to use renewable construction products like wood in larger commercial, residential and mixed use projects. The NEESWood Capstone project tested a seven story mixed use building consisting of a steel framed commercial (retail) main level and six stories of wood framed residential units. This test building was constructed in its entirety within the walls of Earth-Defense. The test building was constructed with many proprietary wood and steel products along with new NEESWood construction methodologies, all of which being beyond the scope of this article.

The portion of the results this test that was of most interest to me as an engineer was the “real life” forces experienced in the structure. As engineers in school we are handed exhaustive volumes of information that we are expected to accept as “the unquestionable truth”. There is an understanding that all of this information has been determined by hundreds of collective years of expert design experience, material testing and are always in a continuous state of refinement. As an engineering student I accepted that this was the adopted standard practice of my trade, but I always wondered how all the design theory I was being fed related to the real world. Hundreds of gauges were installed throughout the Capstone structure to test the forces actually experienced during an earthquake. It was quite satisfying as a design professional to see that the calculated anticipated forces at play in the structure were very close to those actually recorded.

For more detailed information on NEESWood Capstone project please follow this link.

Originally posted 2010-07-15 00:01:06.

Reducing Holdowns Using OSB Exterior Sheathing

Jim Houlette — Sat, 31 Dec 2011 21:20:56 +0000

Tired of all the holdown straps?

You can eliminate many of the metal holdown straps from the upper floor wall to the main floor wall by modifying your OSB wall sheathing layout. When the OSB wall sheathing is continuous over the floor framing section or lapped with the rim board uplift loads can be transferred.

If you are utilizing prefabricated wall panels you can still have the OSB extend to the middle of the rim board. Just have the OSB extend below/above the plates as build in the shop. The only caution is, extra care is needed to prevent the overhanging OSB sheathing from being damaged during shipping.

This concept can also be utilized at the foundation sill plate to help reduce uplift loads that would otherwise require embedded straps such as STHD10RJs. In that situation, cross grain bending is not desired on the sill plate as the load transfers to the anchor bolts. The cross grain bending can be removed from the equation using mud sill anchors (MAS) attached to the exterior face of the OSB sheathing in lieu of anchor bolts. A great solution when utilizing prefabricated walls.

Typically, when building with wood you want many smaller fasteners that distribute the load out evenly rather than a few large fasteners concentrating the load.

EVstudio | Architecture and Engineering | Denver and Evergreen

Originally posted 2009-07-31 00:01:56.

Latch Required in Fire Doors – Opening Protectives

Sean O'Hara — Sat, 31 Dec 2011 21:20:50 +0000

Under the International Building Code, fire doors and swinging pairs of fire doors must be provided with an active bolt that can secure the door when locked.

One spot where this could be easily overlooked is restrooms shared between spaces where the restrooms do not have lockable doors. If a door is in a fire wall, you need to be able to latch it closed.

Originally posted 2009-04-30 23:09:12.

Understanding R-Value and Insulation

evstudio — Sat, 31 Dec 2011 21:20:42 +0000

This post is provided by Earthcore SIPs.

There are many conditions that determine the effectiveness of any building material to provide comfort and energy efficient performance. R-Value is only one of these factors or measurement tools.

R-Value is the measure of resistance to heat flow through the defined material. The higher the R-Value the less heat will transfer through the wall, making the system more energy efficient.

R-Value is determined by testing or by the addition of tested components. When “effective” R-value is used, it represents that at a given condition or circumstance, the system performs the same as a product with the “real” R-value.

It is important to understand the conditions at which the “effective” R-value was determined, and see if your application is the same. For example, a masonry wall may have a high “effective” R-value for a 5 hour test period, but have a very low R-value during a 24 hour test period. Where “real” R-value products will have the same R-value during both test periods.

There are several items to consider when evaluating R-Value and it’s effect on your project

Effective R-Value

An example would be masonry products. Masonry product have a very low R-Value but have a high thermal mass. Foam type products have a high R-value but low thermal mass. There is not a standard measurement or number for the energy effectiveness of thermal mass. While R-value resists the flow of heat, thermal mass delays the transfer of heat but does not reduce it. During a short period, thermal mass has the same “effective” R-value, so it is sometimes advertised with this R-value rating. It is not a real R-value but, under those conditions, an “effective” R-value. Please review other technical bulletins for more details and other related items.

Installed R-Value vs Advertised R-Value

It should be noted that R-Value of an item is the value that was tested in a laboratory and is real, but the item may not perform at the same R-value when installed. Most insulating materials obtain their insulating values from trapped air spaces, often the higher the density of air pockets, the higher the R-value. If these air spaces are compressed, a lower R-value will result. For example, batt type insulation may be rated at R-19 in its free state, but requires a 6 ½” thickness to obtain that value. When this material is installed in a 5 ½” frame cavity, the batt is compressed and the R-value is less than R-19. Likewise, putting two batts in the space for one does not increase insulating value; it might even reduce the R-value. Review the Technical Bulletin on Air Infiltration in Insulation for more related information.

Nonuniform Material

Whole wall R-value is the term used to describe the average R-value for the total wall taking into consideration variations and non-uniformity’s in the insulating material. Often, the R-value of the insulating material is advertised without stating the effect of the total system.

An example would be installing an R-19 batt insulation in a 2×6 frame wall. The resultant “whole wall R-value” is the average of the R-19 insulation and the R-5 stud. Tests have shown that the actual “whole wall R-value” of an R-19 wall system to be R-13.7, much less than the R-19 advertised. This applies to all non uniform wall systems.

The R-value of building materials may be effected or altered by the following items.

Non uniform material
Thermal shorts
Material compression
Air infiltration in the insulation
Humidity
Temperature swing or range of environment
Effects of time and aging.

Along with R-Value, several other factors need to be considered to determine the overall energy efficiency of a building structure.

Thermal Mass
Air infiltration in the building
Radiated heat gains
Internal heat gains
Latent and Sensible heat transfer

Originally posted 2010-03-05 00:01:00.

Separation of Top of Foundation Wall and Adjacent Exterior Grade

Adam Denton — Fri, 09 Dec 2011 23:50:08 +0000

One of the most commonly asked questions to the structural department involved the required distance between the top of a foundation wall and the adjacent exterior grade. The 2009 International Residential Code requires a minimum of 6 inches of separation where brick veneer is not present. The idea here is to provide a buffer zone to help prevent moisture wicking into the timber framing typically framed above residential foundations. Where brick veneer is present this requirement drops down to 4 inches.

The code text reads:

R404.1.6 Height above finished grade. Concrete and masonry foundation walls shall extend above the finished grade adjacent to the foundation at all points a minimum of 4 inches (102 mm) where masonry veneer is used and a minimum of 6 inches (152 mm) elsewhere.

An example of where minimum separation is close, but not met.

Originally posted 2011-04-03 00:01:32.

What in the World is a Ufer Ground?

Adam Denton — Fri, 09 Dec 2011 23:50:01 +0000

In EVstudio’s structural engineering practice this question comes up almost every week. In contemporary construction, a ufer is a concrete encased ground electrode, which is most often a 20 foot long piece of #4 rebar cast into a foundation wall that will protrude from the top of wall so that the structure’s electrical system may attach to it. Technically this falls within the realm of electrical engineering, but enters the realm of structural engineering because the 2008 National Electrical Code requires an installation observation. Because the structural engineer typically will already need to be present on site at some point to observe the rebar construction in the foundation walls many building departments are happy to pass the additional liability on to the structural engineer and require them to observe and document the ufer installation as well.

The ufer was invented during World War II by Herbert Ufer, who was tasked with finding a cheaper alternative to the current method of grounding explosive ordinance storage structures against lighting strikes. The previous grounding method required driving hundreds of feet of electrical ground into the poorly conductive soils found in Arizona. Ufer discovered that due to the naturally high ph levels in concrete (uncured “wet” concrete is caustic and will burn human skin on contact*) the readily available supply of ions will conduct electricity better than almost all soils. The interaction of steel and concrete provide a better ground than the interaction of copper wire and concrete so it was natural connection to utilize the steel reinforcing bars already required of most foundations.

* The author has first-hand knowledge of the validity of this claim.

Originally posted 2011-04-14 00:07:08.

Fastening to Concrete – Wedge Style Expansion Anchors

Adam Denton — Fri, 09 Dec 2011 23:50:00 +0000

A 5/8" diameter wedge style expansion anchor.

There are many situations were it may become necessary to attach a timber ledger to a concrete wall. It is desirable in many new homes to lower the elevation of the finished floor to make a home more wheel chair accessible. An example of the differences between the finished floor elevations that can be achieved with a framing ledger are shown below. Additionally, when an addition is made to a residential home a timber ledger is installed so that the finished floor of the new construction can match the finished floor elevation of the existing construction while utilizing the existing foundation wall.

Conventional Floor Framing vs. Ledgered Floor Framing

Wedge style expansion anchors work because of the friction forces developed between the studded collar (see photo at top) and the concrete. To begin a typical installation a hole must first be drilled into the concrete. All manufacturer’s instructions for hole size and depth should be followed carefully because the recommendations will vary between bolts sizes and manufacturers. Once a hole is drilled and cleaned the anchor may be driven into the hole with a hammer. The studs on the collar are slightly larger than the widest diameter of the bolt so initial contact with the concrete is only at these areas. Once the bolt is driven to its specified depth a pre-drilled timber ledger may be installed over the bolts. Finally, the nuts (with supplied washer) may be installed. As the nut is tightened, the studded collar with catch on the edges of the hole in the concrete and will be forced onto the wedge. The collar will expand as it is driven onto the wedge creating a greater frictional force against the concrete. With the nut installed to the proper torque the anchor may be safely loaded to the manufacturer’s design specifications.

Originally posted 2010-07-30 23:04:52.